The tabloids have their man. Abu Hamza al-Masri, the one-eyed, hook-handed villain from Central Casting, is finally behind bars, fighting extradition to America on terrorism charges. The only disappointment for those who have demanded for years that the inflammatory preacher be taken off the streets is that the US authorities have promised not to execute him - if found guilty, of course.

The arrest of the 47-year-old Islamist, who says his disabilities are the result of a mine-clearing accident in Afghanistan in 1993, will bring the first test of a new "fast track" extradition agreement reached between Britain and the US after the September 2001 attacks. The Home Secretary, David Blunkett, says he wants Mr Hamza sent to the US as quickly as possible, but the courts may take a different view as the Egyptian-born former nightclub bouncer seeks to appeal if the extradition request is approved. The case could end up at the European Court of Human Rights, fought all the way - to the fury of the tabloids - on legal aid.

The Americans have prepared an 11-count indictment against Mr Hamza which depicts him as a mastermind of terrorism. It says he tried to set up a training camp for "violent jihad" at a ranch in Oregon and planned the kidnap of 18 Westerners in Yemen in 1998, an episode that ended in the deaths of four hostages. The kidnappers were seeking the release of Islamists including Abu Hamza's son and godson, who were later jailed for plotting to attack Western targets in Yemen.

"Hamza is the real deal," Raymond Kelly, New York City's police commissioner, told The New York Times. "He is suspected of providing material support to trainees in Osama bin Laden's terrorist camps, as well as dispatching associates from England to help establish a jihad training site on US soil. Think of him as a freelance consultant to terrorist groups worldwide."

American officials have frequently expressed surprise and frustration that Abu Hamza has been free to walk the streets of London, despite his open extremism and bloodcurdling speeches, in which he has reportedly supported blowing up airliners, committing suicide attacks in Britain and killing all Jews above the age of 15. "Every single terrorist suspect who has passed through Britain has left a trail of slime back to Hamza," said Andrew Dismore, the Labour MP for Hendon, who has long campaigned against him.

But last week Mr Blunkett repeated the official line, insisting Britain did not have evidence against the preacher that was admissible in court. "Had we evidence in this country of a crime here, then of course the police and the Attorney General would have taken action," he said. The US says it has evidence of Mr Hamza's involvement in the Yemen kidnapping - where three of the four hostages who died were British - from an electronic intercept, but Mr Blunkett said: "We do not use intercept in open court."

Why have the British authorities seemed so reluctant to pursue Abu Hamza? Is it because they see him as a buffoon who revels in his image as a hate figure, and who would be more dangerous if allowed to pose as a martyr? Or, as some in the US and France have claimed, because there is an unspoken deal allowing extremists like him to operate here, as long as there are no attacks in Britain?

Yet another theory has it that he is useful to the security services because he attracts young hotheads who are potential recruits for terrorism by more shadowy figures. At least the authorities know where to find them, according to this view; with their mentor off the scene they might disperse and be less easy to keep under observation.

It was never going to be possible, however, to ignore the clamour for action indefinitely. A British citizen through his marriage to a British woman he has since divorced, he began preaching at the Finsbury Park Mosque in London after returning from Afghanistan. His ability to speak English and inflammatory rhetoric attracted young British-born Muslims, but also brought heavy media attention, to the despair of more moderate Muslims who say his influence is marginal.

Since September 2001, however, he has been linked to Feroz Abbasi, one of the Britons held at Guantanamo Bay in Cuba, whose mother believes her son was "brainwashed" by Mr Hamza during his visits to the mosque; the "shoe bomber", Richard Reid, and the British would-be suicide bomber Omar Sharif, who was involved in an attack in Tel Aviv.

Forced out into the street to preach since early last year, and fighting an attempt by Mr Blunkett to strip him of his citizenship, Mr Hamza now faces claims from another former acolyte, James Ujaama, that he sent two associates to a ranch near Bly, Oregon, to investigate setting up a jihad training camp in 1999. According to Ujaama, who received a light sentence in Seattle in return for his testimony, the scheme fell through for lack of recruits.

If the case succeeds, it would be the first proof that Abu Hamza intended turning his words into action. Conveniently for US and British governments both facing elections in the next 12 to 15 months, it may take considerably longer to come to trial. And in the meantime the turbulent preacher is out of the way.